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If the output is digital does the player make any difference to the so
xnor
post Jul 31 2012, 23:21
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QUOTE (yourlord @ Jul 31 2012, 23:33) *
[...] the delivered data should be identical [...] so long as it's sent via a reliable link or protocol.

For most DACs with an USB receiver this premise is not true.

Unlike TCP, there is no retry if delivery of data failed, no guarantee of delivery. In fact, isochronous transfer is unidirectional.

(Btw, when talking about USB audio streaming I don't mean listening to an internet radio station..)

This post has been edited by xnor: Jul 31 2012, 23:22
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mzil
post Aug 1 2012, 00:16
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The signal the HDMI output sends gets transfered pristinely and without degradation, however that signal is not a bit for bit identical copy of the file on the disc/hard drive, it is a converted version of that file, which to the best of my knowledge can not be reassembled on the receiving end to make an exact copy of the file from the original source. [Even if there weren't copy protection schemes in place to prevent it and pretending for the moment that there were stand alone recorders with HDMI in]. HDMI streaming is not the same as a USB file transfer.

I'm not arguing that the difference from device to device is audible, however. I'm just saying it's not a bit for bit accurate copy of the original file and may vary from device to device, which was the OP's question.

"Since all of the content will be transferred digitally to your display, this should result in perfect picture quality with no issues since "bits are bits", right? Unfortunately the reality is far more complex than this, and there are many factors that can come into play."

That quote is from this magazine and the article shows how there are many changes to the HDMI signal outputs between, for example, an OPPO and a Sony machine (that fails in some regards compared to the OPPO), using a very pricey Quantum Data HDMI Analyzer, however they unfortunately dont address the audio over the HDMI.

I guess everyone here (but me) thinks the audio is simply an unmodified S/PDIF signal and interchangeable between devices, however I'm not so sure. Machines modify their HDMI out video signals according to that magazine, so how can we be so sure they don't also manipulate their HDMI out audio signals?

This post has been edited by mzil: Aug 1 2012, 00:19
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yourlord
post Aug 1 2012, 03:33
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QUOTE (mzil @ Jul 31 2012, 19:16) *
The signal the HDMI output sends gets transfered pristinely and without degradation, however that signal is not a bit for bit identical copy of the file on the disc/hard drive, it is a converted version of that file, which to the best of my knowledge can not be reassembled on the receiving end to make an exact copy of the file from the original source. [Even if there weren't copy protection schemes in place to prevent it and pretending for the moment that there were stand alone recorders with HDMI in]. HDMI streaming is not the same as a USB file transfer.


You are correct. The file on the disc is compressed using a lossy codec. I'm not arguing that the data transmitted has any resemblance to the file on the disc. I'm saying the data transmitted, which is the decompressed output from the decoder in the player, will arrive perfectly intact at the destination.

If the decoder in the player has a bug or other issue in it's implementation then that decoded output may differ from another player, but either way HDMI will faithfully deliver the decoder output to the receiver.
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andy o
post Aug 1 2012, 15:46
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QUOTE (xnor @ Jul 31 2012, 12:07) *
I don't know if the same is true for HDMI. Old receivers had horrible jitter problems but I guess this problem was fixed one or two years ago.

Could you elaborate on this, please?
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xnor
post Aug 1 2012, 16:37
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For example the Yamaha RX-V3900 was measured to have 7660 ps of jitter.
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mzil
post Aug 1 2012, 17:07
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^Do you have any evidence that level is audible to humans under controlled conditions?

All I know is this study which suggests < 250 ns (250,000 ps) is safe. The Yamaha easily qualifies.

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xnor
post Aug 1 2012, 17:17
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Nope and that's why I didn't make that claim, but such amounts of jitter have a big measurable negative effect on SNR. I can imagine that it could be audible with highly dynamic recordings if you turn up the volume quite a bit.

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mzil
post Aug 1 2012, 17:31
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If you are allowed to turn up the volume and listen to the noise floor, almost everything sounds different! Suddenly comparing a device with a noise floor 100 dB down becomes discernable from one that's 102 dB, with the right material and fast A/B switching, but in real world use it is completely meaningless and undetectable. [Not hard to believe since all of us would have no problem detecting a 2 dB change in audible hiss in real world conditions.]

"Poor" low level linearity down at those levels [when greatly amplified] also becomes audible, but similarly, in real world use, is completely meaningless and undetectable.

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greynol
post Aug 1 2012, 17:59
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Do DACs matter?

Perhaps, but if you can't demonstrate audible differences through double-blind testing then for practical purposes they don't, at least not as far as this forum is concerned.

This post has been edited by greynol: Aug 1 2012, 18:01


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Roseval
post Aug 1 2012, 18:13
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QUOTE (xnor @ Jul 31 2012, 23:21) *
Unlike TCP, there is no retry if delivery of data failed, no guarantee of delivery. In fact, isochronous transfer is unidirectional.


The first part is correct.
As an isochronous stream is a soft real time stream, a retry will always be too late.
However USB in isochronous mode does reserve the appropriate bandwidth.
So delivery is guaranteed downstream but delivering of the right bits is not

The second part is not correct.
One can combine isochronous (thatís the way USB audio works) with 3 different type of synchronization.
In case of synchronous or adaptive synchronization, the protocol is used unidirectional (the DAC adapts its clock speed to the incoming data stream).
In case of asynchronous synchronization a feedback loop is established controlling the amount of data send by the PC.
This allows the DAC to run with a fixed clock.
In this case the protocol is used bi-directional.

http://thewelltemperedcomputer.com/KB/USB.html


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xnor
post Aug 1 2012, 18:34
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QUOTE (Roseval @ Aug 1 2012, 19:13) *
As an isochronous stream is a soft real time stream, a retry will always be too late.

It probably would be too late, but typically there are no retries (see adaptive below).

QUOTE
However USB in isochronous mode does reserve the appropriate bandwidth.
So delivery is guaranteed downstream but delivering of the right bits is not

If frames need to arrive every ms but do not it doesn't matter how much bandwidth is reserved. Also, most glitches occur because data doesn't arrive in time (DPC latency on Windows), not because of flipped bits.

The second part is not correct.
QUOTE
One can combine isochronous (that’s the way USB audio works) with 3 different type of synchronization.

Theoretically, yes, but most USB audio devices function in "isochronous adaptive" mode.

Devices using "isochronous transfer with asynchronous synchronization" are typically simply called 'asynchronous'. I guess I should have been more pedantic with the terms I used before. Noted.

This post has been edited by xnor: Aug 1 2012, 18:37
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greynol
post Aug 1 2012, 18:40
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QUOTE (xnor @ Aug 1 2012, 10:34) *
I guess I should have been more pedantic with the terms I used before.

...as should I have when talking about double-blind testing trumping measurements as a means to demonstrate audible differences. Noted. wink.gif

This post has been edited by greynol: Aug 1 2012, 18:42


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Roseval
post Aug 1 2012, 18:50
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QUOTE
If frames need to arrive every ms but do not it doesn't matter how much bandwidth is reserved. Also, most glitches occur because data doesn't arrive in time (DPC latency on Windows), not because of flipped bits.


It works slightly different.
The frames always arrive in time, thatís the way USB works.
The bandwidth is reserved on the hub to avoid interference of other USB devices.
But this is downstream not upstream.
The frames will always arrive in time but you might get glitches due to an insufficient amount of data in the frame e.g. due to DPC latency upstream

BTW: a lot of new USB DACs support async: http://thewelltemperedcomputer.com/HW/USB_DAC_Async.htm

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pdq
post Aug 1 2012, 19:51
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QUOTE (xnor @ Aug 1 2012, 12:17) *
Nope and that's why I didn't make that claim, but such amounts of jitter have a big measurable negative effect on SNR. I can imagine that it could be audible with highly dynamic recordings if you turn up the volume quite a bit.

On the contrary, jitter noise is proportional to the amplitude of the signal, so in very quiet passages the jitter noise also becomes much smaller. Jitter has no effect whatever on silence.
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andy o
post Aug 1 2012, 20:34
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QUOTE (xnor @ Aug 1 2012, 08:37) *
For example the Yamaha RX-V3900 was measured to have 7660 ps of jitter.

One problem with one receiver doesn't jibe with this statement though: "Old receivers had horrible jitter problems but I guess this problem was fixed one or two years ago".

(If that was even a problem, as others are saying.)

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greynol
post Aug 1 2012, 20:38
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How about the word horrible?

EDIT: Just saw your edit:
QUOTE (andy o @ Aug 1 2012, 12:34) *
(If that was even a problem, as others are saying.)


This post has been edited by greynol: Aug 1 2012, 20:39


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Arnold B. Kruege...
post Aug 2 2012, 18:35
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QUOTE (db579 @ Jul 31 2012, 08:56) *
So with that in mind if you wanted portable audiophile sound quality, all you'd need is any flac or wav player (quality not particularly important) with a digital out, good headphones and a good portable DAC? Does such a DAC exist? How do they compare to AV receivers?


I often use a Behringer UCA 202 ($30) with older laptops that have problematical audio interfaces. Its headphone amp leaves something to be desired with some headphones. The FIIO E7 seems to have a better headphone amp at a far higher cost, particularly in the area of providing a consistent low source impedance.

In general good portable equipment such as the Sansa Clip/Fuze perform about as well as a good AVR, other than power output. The headphone jack on a Clip/Fuze may outperform some AVR headphone jacks, particularly in the area of providing a consistent low source impedance.
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Arnold B. Kruege...
post Aug 2 2012, 18:41
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QUOTE (Roseval @ Aug 1 2012, 13:50) *
QUOTE
If frames need to arrive every ms but do not it doesn't matter how much bandwidth is reserved. Also, most glitches occur because data doesn't arrive in time (DPC latency on Windows), not because of flipped bits.


It works slightly different.
The frames always arrive in time, thatís the way USB works.
The bandwidth is reserved on the hub to avoid interference of other USB devices.
But this is downstream not upstream.
The frames will always arrive in time but you might get glitches due to an insufficient amount of data in the frame e.g. due to DPC latency upstream

BTW: a lot of new USB DACs support async: http://thewelltemperedcomputer.com/HW/USB_DAC_Async.htm



As far as I can tell, the Asynch DAC issue is the latest in an long history of efforts by audio's high end to justify higher prices for what has largely become a commodity item.

I'd like to see someone make a Behringer UCA 202 (limited to line level loads) or Fiio E7 flunk an ABX test comparing it to some highly-reviewed (technically) asynch DAC.
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Arnold B. Kruege...
post Aug 2 2012, 18:50
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QUOTE (xnor @ Aug 1 2012, 12:17) *
Nope and that's why I didn't make that claim, but such amounts of jitter have a big measurable negative effect on SNR. I can imagine that it could be audible with highly dynamic recordings if you turn up the volume quite a bit.


I don't know about SNR, but if it is really humongous, jitter can have an bad effect on THD+N. Not because it creates THD, but because the sidebands that jitter does create might be confused by the measuring technique with noise or harmonics.

As correctly stated by others, jitter has no effect on the noise floor again unless it becomes really huge and creates clicks and pops.

What's interesting is that as far as I can see, none of the technical data shown at the well-tempered computer page linked out of this thread actually shows jitter.

BTW I have heard a lot of jitter in my day, most intentionally created to mimic what I see in test reports, but at levels high enough to actually hear. Jitter seems to have a characteristic, generalizible sound. In general the subjective comments by high end reviewers don't seem to describe what I hear.

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xnor
post Aug 2 2012, 18:50
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As I said, isochronous (adaptive) transfer can work perfectly fine.
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Arnold B. Kruege...
post Aug 2 2012, 18:55
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QUOTE (xnor @ Aug 2 2012, 13:50) *
As I said, isochronous (adaptive) transfer can work perfectly fine.


I would like to see a real-world reliable test that shows it working any way but fine.

All we seem to have is these anecdotes.
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greynol
post Aug 2 2012, 18:58
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...and poor subject/verb agreement, lol.

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Roseval
post Aug 2 2012, 19:05
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A test by Jim Lesurf: http://www.audiomisc.co.uk/Linux/Sound3/TimeForChange.html


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Arnold B. Kruege...
post Aug 2 2012, 19:26
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QUOTE (Roseval @ Aug 2 2012, 14:05) *


* no reliable listening test

* What do the spurious responses he measured mean given that they are given in parts per BILLION?

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xnor
post Aug 2 2012, 21:21
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QUOTE (Arnold B. Krueger @ Aug 2 2012, 19:55) *
All we seem to have is these anecdotes.


So you think a lot of people, including me (on my old notebook anyway), imagine audio glitches like VERY ANNOYING clicks or drop-outs with USB DACs? Screenshots of DPC latency measurements that clearly show that the hardware isn't able to stream audio glitch-free are anecdotes too?

Just because you haven't seen it yourself doesn't mean it's not real.

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